A component of current probabilistic seismic design frameworks is a demand model relating the probability of exceeding certain demand measures given expected seismic hazard. This demand model can be formulated using two analysis methods, Probabilistic Seismic Demand Analysis and Incremental Dynamic Analysis. The first method attempts to represent seismicity through a wide selection of many ground motions, grouped into bins. The latter method achieves the same by stepwise incrementation of a select few ground motion records. Comparison of resulting Probabilistic Seismic Demand Models relating structural demand measures to quantified measures of intensity yield information as to the equivalency of the two methods and instances when they can be used interchangeably. The demand models developed in this paper are for typical California highway overpass bridges, using the variation of the column diameter design parameter as an illustrative case of the applicability of the methods.
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